"So you really propose to launch the _Snowbird_ in this way?" asked Jack. "We will be shot into the air. If you are sure of your machine, I am sure of my catapult, and we will try the two contrivances together." In the morning all rose bright and early and prepared the _Snowbird_ for her trial flight. Washington White had indeed disappeared--possibly in search of his Shanghai rooster--and Andy Sudds was off on a hunt. Therefore the professor and his two young comrades essayed the trip alone. Jack and Mark tossed a coin to see who should first guide the great air machine, and Mark won the preference. He, as well as his chum and the professor, had already donned their aeronautic uniforms, and he now strapped himself into the pilot's seat. The steering apparatus, the levers that controlled the planes, and the motor switch were all under his hand. While in flight the _Snowbird_ need be under the control of but one person at a time. The professor had rigged his catapult so that he could release the trigger from the flying machine. Mark said he was ready; the professor reached for the cord which would release the trigger. "Start your motor, Mark, a fraction of a second before I release the compressed air," commanded Mr. Henderson. "Now!" The motor of the flying machine buzzed faintly. Jack's eyes were on the speed indicator. He suddenly felt the great, quivering flying machine, which had been run out of the hangar on to the steel plank of the catapult, lurch forward. The feeling affected him just as the sudden dropping of an elevator from a great height affects its passengers. The finger of the speed indicator whirled and marked forty miles an hour ere the flying machine left the steel plank, and shot into the air with the fearful force of the compressed air behind it. Both Mark and Jack were well used to guiding aeroplanes and other air machines. But this start from the ground was much different from the easy, swooping flight of an airship as usually begun. Like an arrow the _Snowbird_ was shot upward on a long slant. It was a moment ere Mark got the controls to working. The propellers were, of course, started with the first stroke of the motor. But Mark Sampson was nervous; there was no denying that. At the instant when the nose of the airship should have been raised, so as to clear the tops of the forest trees and every building on the Henderson place, Mark instead guided the rapidly flying _Snowbird_ far to the left. It skimmed the corner of the stable by a fraction of a foot, and Jack yelled: "Look out!" His cry made Mark even more nervous. The tall water-tank and windmill were right in line. Before the young aviator could swerve the flying machine to escape the vane upon the roof of the tower, and the long arms of the mill, they were right upon these things!